Machines such as, for example, excavators, loaders, dozers, motor graders, and other types of heavy equipment use multiple actuators supplied with hydraulic fluid from a pump on the machine to accomplish a variety of tasks. These actuators are typically velocity controlled based on an actuation position of an operator interface device. For example, an operator interface device such as a joystick, a pedal, or another suitable operator interface device may be movable to generate a signal indicative of a desired velocity of an associated hydraulic actuator. When an operator moves the interface device, the operator expects the hydraulic actuator to move at an associated predetermined velocity. However, when multiple actuators are simultaneously operated, the hydraulic fluid flow from a single pump may be insufficient to move all of the actuators at their desired velocities. Situations also exist where the single pump is undersized and the desired velocity of a single actuator requires a fluid flow rate that exceeds a flow capacity of the single pump.
One method of selectively combining the hydraulic fluid flow from multiple pumps to move a single actuator is described in U.S. Pat. No. 4,528,892 (the '892 patent) issued to Okabe et al. on Jul. 16, 1985. The '892 patent describes a machine hydraulic circuit system having a first valve group and a second valve group. The first valve group includes a swing valve, a first boom valve, a first arm (e.g., stick) valve, a first bucket valve, and a left travel valve. The swing valve and first boom valve are connected in parallel, and together are connected in interrupted series with the first arm valve, first bucket valve, and left travel valve. The second valve group includes a right travel valve, a second arm valve, a second bucket valve, and a second boom valve. The second arm valve, second bucket valve, and second boom valve are connected in parallel, and together are connected in interrupted series with the right travel valve. The first and second arm valves function to supply fluid from a first pump and a second pump, respectively, to an arm actuator. The first and second bucket valves function to supply fluid from the first and second pumps, respectively, to a bucket actuator. The first and second boom valves function to supply fluid from the first and second pumps, respectively, to a boom actuator. The left and right travel valves function to supply fluid from the first and second pumps, respectfully, to left and right travel actuators. A selector valve selectively fluidly couples the first and second valve groups in response to a desired travel operation.
The location of each of the control valves within the hydraulic circuit system of the '892 patent is such that, when initiating a swing, boom, arm, or bucket movement, without travel of the machine, a combined fluid flow from the first and second pumps powers the movement. In addition, when turning to the left and simultaneously initiating a swing, boom, arm, or bucket motion, fluid from both first and second pumps still powers the movement. However, when turning to the right, although fluid from the first pump is available to the swing, boom, arm, and bucket actuators, fluid from the second pump is only available to the left travel actuator. Further, when traveling straight, although fluid from the first pump is available to the swing, boom, arm, and bucket actuators, fluid from the second pump is only available to the left and right travel actuators.
Because of the interrupted series relationships described above with regard to the '892 patent, if independent swing and boom motions are desired, an operator must take care to manipulate the control lever such that only one of the first and second boom control valves is actuated (e.g., move the control lever less than halfway through its available range of motion). During a swing or boom motion, regardless of the care of the operator or the desired velocity, fluid from only the second pump is only ever available for a stick function.
Although the hydraulic circuit system of the '892 patent may combine pump fluid flows to improve control of some functions, operation of the machine may be inconsistent and limited. In particular, because fluid flow is available from both pumps for swing, boom, arm, and bucket motions during a left turn, but only available from a single pump during a right turn, control of the machine may be difficult and confusing. In addition, the fluid flow available during a right turn may be insufficient for some operations.
Further, because of the limitations of the hydraulic circuit system of the '892 patent and the care that must be taken when operating the associated machine, operational costs of the machine may be substantial. In particular, the care required of the operator to independently and simultaneously initiate a swing and boom movement, may necessitate the use of highly-trained, experienced, and costly operators to run the machine. In addition, there may be situations when a combined pump flow for an arm movement is desired simultaneous to a boom or swing movement. Because these simultaneous operations are unavailable from the machine of the '892 patent, efficiency and production of the machine may be inadequate for certain applications.
In addition, the hydraulic circuit system of the '892 patent may be expensive. Specifically, because two valves are required to provide combined flows to each fluid actuator, the cost of the system may be substantial.
The disclosed control system is directed to overcoming one or more of the problems set forth above.